In various contexts, it is required that substantially clear media or sample containers be examined for the presence of a precipitate, bacterial growth, or the like. Many devices exist to aid in this process. Generally the clear media or sample containers are illuminated from the side by a light source so shielded as to not be observable directly from the viewer's location. The clear media or a sample container so side lighted is then viewed against a dark background with the result that light scattered toward the viewer by suspended material may be seen more easily. Examples of such devices include Levy, U.S. Pat. No. 2,342,409; Danti, et al., U.S. Pat. No. 3,652,169; Bergeron, U.S. Pat. No. 3,712,746; Vanden Broek, et al., U.S. Pat. No. 4,099,881; and Clark, et al., U.S. Pat. No. 4,457,894. McFadden, U.S. Pat. No. 4,221,867 is such a viewer specifically adapted for use with microtiter plates having rows of wells, each of which wells contains a sample to be viewed. McFadden shows an array of vanes or baffles so situated relative to each other that an entire row of wells may be viewed from above simultaneously while being lit from two sides.
It is often necessary in certain procedures that the wells of a microtiter plate be examined first in such a way that suspended material or small buttons of precipitate may easily be seen and then in such a way that the colors of the media in each well can be evaluated. Side lighting against a dark background is useful for the first type of examination but is inadequate for the second. In addition, it is an advantage to be able to examine a large number of such wells at the same time without the need to move the microtiter plate. Thus, it is sometimes desirable to be able to examine a block or other array of such wells and to change with facility between alternate viewing modes in which the wells of a plate are examined both for color and the presence of bacterial growth as evinced by turbidity, a precipitate, or the like.